Astronomers Discover Upper Limit for Mass of Giant Black Holes

There appears to be an upper limit to how big the universe's most massive black holes can get, according to new research by astrophysicists from the University of Hawaii at Manoa and Yale University. This limit is 10 billion times the mass of the Sun or about one percent of the total mass of the giant galaxies in which these black holes are found.

Once considered rare and exotic objects, black holes are now known to exist throughout the universe, with the most massive found at the centers of the largest galaxies. These "ultra-massive" black holes have been shown to have masses upwards of one billion times that of our own Sun. Now, Ezequiel Treister, a Chandra postdoctoral fellow at the University of Hawaii and Priyamvada Natarajan, an associate professor of astronomy and physics at Yale University, have shown that even the biggest of these gravitational monsters can't keep growing forever. Instead, they appear to curb their own growth—once they accumulate about 10 billion times the mass of the Sun.

These ultra-massive black holes, found at the centers of giant elliptical galaxies in huge galaxy clusters, are the biggest in the known universe. Even the large black hole at the center of our own Milky Way galaxy is thousands of times less massive than these behemoths. But these gigantic black holes, which accumulate mass by sucking in matter from neighboring gas, dust and stars, seem unable to grow beyond this limit regardless of where—and when—they appear in the universe. "It's not just happening today," said Natarajan. "They shut off at every epoch in the universe."

The study, to appear in the Monthly Notices of the Royal Astronomical Society (MNRAS), represents the first time an upper mass limit has been derived for black holes. Natarajan and Treister used existing optical and X-ray data of these ultra-massive black holes to show that, in order for those various observations to be consistent, the black holes must essentially shut off at some point in their evolution. "Getting a complete observational census of black holes from X-ray data, using the deepest observations with the Chandra Observatory, was an important piece in this puzzle," said Treister.

Several groups have suggested possible growth control mechanisms. One possible explanation, derived by Natarajan in earlier work, is that the black holes might eventually reach the point when they radiate so much energy as they consume their surroundings that they end up interfering with the very gas supply that feeds them, which may also interrupt star formation in the vicinity. The new findings have implications for the future study of galaxy formation, since many of the largest galaxies in the universe appear to co-evolve along with the black holes at their centers.

"Evidence has been mounting for the key role that black holes play in the process of galaxy formation," said Natarajan. "But it now appears that they are likely the prima donnas of this space opera."

The authors of the paper are Priyamvada Natarajan (Yale University and the Radcliffe Institute for Advanced Study) and Ezequiel Treister (Institute for Astronomy, University of Hawaii).

Figure 1. Image of the giant elliptical galaxy ESO 325-G004 taken by the Hubble Space Telescope using the Advanced Camera for Surveys. This giant galaxy, with a mass of about 100 billion solar masses, is located in the center of the galaxy cluster Abell S0740, 450 million light-years away from us in the Centaurus constellation. Giant elliptical galaxies, typically found in the centers of galaxy clusters, like ESO 325-G004 are the hosts of ultra-massive black holes with masses larger than five billion solar masses. Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA). Acknowledgment: J. Blakeslee (Washington State University)

Founded in 1967, the Institute for Astronomy at the University of Hawaii at Manoa conducts research into galaxies, cosmology, stars, planets, and the sun. Its faculty and staff are also involved in astronomy education, deep space missions, and in the development and management of the observatories on Haleakala and Mauna Kea.

Established in 1907 and fully accredited by the Western Association of Schools and Colleges, the University of Hawaii is the state's sole public system of higher education. The UH System provides an array of undergraduate, graduate, and professional degrees and community programs on 10 campuses and through educational, training, and research centers across the state. UH enrolls more than 50,000 students from Hawaii, the U.S. mainland, and around the world.

Support for this work was provided by the National Aeronautics and Space Administration through Chandra Postdoctoral Fellowship Award Number PF8-90055 issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060

The Hubble Space Telescope is operated by the Space Telescope Science Institute with funding from NASA.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author[s] and do not necessarily reflect the views of the Smithsonian Astrophysical Observatory or the National Aeronautics and Space Administration.